The amphetamine analog 3,4- methylenedioxymethamphetamine (MDMA) continues to be a popular drug of abuse despite evidence in animals and humans that this agent produces long-term toxicity to serotonin (5-HT) neurons. However, beyond this well-established finding, the mechanisms through which MDMA produces 5-HT neurotoxicity remain unknown. Several lines of evidence suggest that oxidative stress contributes to the process of MDMA-induced 5-HT toxicity. The intent of the present study is to elucidate the processes, proceeding or subsequent to, the induction of oxidative stress that are the determinants of MDMA-induced 5-HT neurotoxicity. A central focus of this application is the hypothesis that MDMA toxicity in the hippocampus, in contrast to the striatum, results, in part, from excessive extracellular concentrations of glutamate. Specifically, it is hypothesized that the long-term depletion of 5-HT produced by MDMA in the hippocampus results from a glutamate-mediated increase in nitric oxide formation and a subsequent impairment of mitochondrial function. Impaired mitochondrial function provides a feed forward mechanism for the further generation of free radicals and ensuing structural damage to 5-HT terminals and depletion of 5-HT. The specific aims of the proposal are to utilize in vivo microdialysis, biochemical experiments and immunohistochemical studies to: 1) assess the contribution of glutamate to the process of MDMA toxicity in the hippocampus and establish the mechanism underlying the MDMA-induced increase in extracellular glutamate, 2) evaluate potential mechanisms through which MDMA increases nitric oxide formation, 3) determine whether increased nitric oxide formation contributes to the MDMA-induced inhibition of mitochondrial function and 4) assess the extent and mechanism by which MDMA promotes the cleavage of the cytoskeletal proteins tau and spectrin. The linkage of the processes of oxidative damage and mitochondrial impairment to the long-term effects of MDMA on 5-HT terminals has significant implication for drug-induced neurodegeneration and risks this may pose to human health.